I really like Drapion with cross poison, night slash, sniper, and razor claw to use for a sweeper in RU, but is he good or is he worth it in OU? I am considering using him for a team.
No. Lacks the Speed and Power to pull off Sweep, shallow, predictable movepool, and is outclassed by many brother Dark Type. Physical Dark Type I'd suggest is Weavile.
Weavile @ Life Orb Trait: Pressure EVs: 4 HP / 252 Atk / 252 Spe Jolly Nature (+Spe, -SpA) - Ice Shard - Ice Punch - Night Slash - Low Kick
In theory, Drapion could sweep in OU, but it is greatly outclassed in the tier by Hydreigon. In RU, Drapion can hold his own as a bulky sweeper, but probably shouldn't be used in OU. Why make him look bad, when he has so much RU potential?
Hydreigon @ Choice Scarf Trait: Levitate 252 Spd / 252 SAtk / 4 HP Dark Pulse Flamethrower/Fire Blast Draco Meteor U-Turn/Focus Blast
Boss.